Balanced high-frequency device and balanced high-frequency circuit using the same

ABSTRACT

A balanced high-frequency device includes a balanced element; at least one balanced terminal connected to the balanced element; a phase circuit having at least first, second, and third impedance elements, and electrically connected between the balanced element and the balanced terminal. The first impedance element and the second impedance element are connected between the balanced terminals in series, the connection point between the first impedance element and the second impedance element is grounded through the third impedance element, a series resonant circuit is formed by the first impedance element and the third impedance element. A series resonant circuit is formed by the second impedance element and the third impedance element, and an impedance to a differential signal component in the passing band of the balanced elements of the first and second impedance elements is set so as to increase to the ground plane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a balanced high-frequency device suchas an surface acoustic wave filter or a high-frequency amplifier, abalanced high-frequency circuit using the balanced high-frequencydevice, a phase circuit, and a balance-characteristic improving method.

2. Related Art of the Invention

Because mobile communication has recently advanced, improvement ofperformances of and downsizing of a device used are expected. Moreover,to improve noise characteristics to crosstalk between devices, balancingof a filter and a semiconductor device used for RF stage is progressedand a preferable balance-characteristic is requested. For a filter, ansurface acoustic wave filter is more widely used. Particularly, in thecase of a longitudinally coupled mode surface acoustic wave filter,balance-unbalance conversion can be easily realized because of theconfiguration of an IDT electrode and small loss, high attenuation, andpreferable balance-characteristic are expected for an RF-stage filterhaving balanced input and output terminals.

A conventional balanced high-frequency device is described below. FIG.28 shows a configuration of a conventional balanced high-frequencydevice 2801. The balanced high-frequency device 2801 is constituted byan input terminal IN serving as a unbalanced input/output terminal andoutput terminals OUT1 and OUT2 serving as balanced input/outputterminals.

Moreover, in the case of a balanced high-frequency device, impedancematching is necessary. FIGS. 29(a) and 29(b) shows configurations of aconventional balanced high-frequency devices respectively having amatching circuit. In FIG. 29(a), a balanced high-frequency device 2901is constituted by an input terminal IN serving as an unbalancedinput/output terminal and output terminals OUT1 and OUT2 serving asbalanced input/output terminals. Moreover, a matching circuit 2902 isconnected between the output terminals OUT1 and OUT2. Moreover, in FIG.29(b), a balanced high-frequency device 2903 is constituted by an inputterminal IN serving as an unbalanced input/output terminal and outputterminals OUT1 and OUT2 serving as balanced input/output terminals.Furthermore, matching circuits 2904 and 2905 are connected between theoutput terminals OUT1 and OUT2 and ground planes respectively. This typeof the matching circuit is used to match a balanced high-frequencydevice with the characteristic impedance of a balanced input/outputterminal.

As an example of the above balanced high-frequency device, aconventional surface acoustic wave filter is described below. FIG. 30shows a block diagram of an surface acoustic wave filter 3001 having abalanced input/output terminal. In FIG. 30, the surface acoustic wavefilter 3001 is constituted on a piezoelectric substrate 3002 by first,second, and third inter-digital transducer electrodes (hereafterrespectively referred to as IDT electrode) 3003, 3004, and 3005 andfirst and second reflector electrodes 3006 and 3007. One-hand electrodefinger of the first IDT electrode 3003 is connected to an outputterminal OUT1 and the other-hand electrode finger of the first IDTelectrode 3003 is connected to an output terminal OUT2. Moreover,one-hand electrode fingers of the second and third IDT electrodes 3004and 3005 are connected to an input terminal IN and the other-handelectrode fingers of the electrodes 3004 and 3005 are grounded. By usingthe above configuration, it is possible to realize an surface acousticwave filter having an unbalanced-balanced input/output terminal.Moreover, in the case of the surface acoustic wave filter in FIG. 30,impedances of the input and output terminals are respectively designedas 50 Ω.

Moreover, a conventional surface acoustic wave filter is described belowas an example of a balanced high-frequency device having a matchingcircuit. FIG. 31 shows a block diagram of an surface acoustic wavefilter 3101 having a matching circuit. In FIG. 31, the surface acousticwave filter 3101 is constituted on a piezoelectric substrate 3102 byfirst, second, and third inter-digital transducer electrodes (hereafterrespectively referred to as IDT electrode) 3103, 3104, and 3105 andfirst and second reflector electrodes 3106 and 3107. The first IDTelectrode 3103 is divided into two divided IDT electrodes. One electrodefinger of a first divided IDT electrode 3108 is connected to an outputterminal OUT1, one electrode finger of a second divided IDT electrode3109 is connected to an output terminal OUT2, and the other-handelectrode fingers of the first and second divided IDT electrodes areelectrically connected. Moreover, one-hand electrode fingers of thesecond and third IDT electrodes 3104 and 3105 are connected to an inputterminal IN and the other-hand electrode fingers of the electrodes 3104and 3105 are grounded. Furthermore, an inductor 3110 is connectedbetween output terminals as a matching circuit. By using the aboveconfiguration, it is possible to realize an surface acoustic wave filterhaving an unbalanced-balanced input/output terminal. Furthermore, in thecase of the surface acoustic wave filter in FIG. 31, impedances of inputand output terminals are designed as 50 Ω for the input side and as 150Ω for the output side. Therefore, the filter has an impedance conversionfunction.

FIGS. 32(a) to 32(c) show characteristic diagrams of a conventionalsurface acoustic wave filter of a 900-MHz band shown in FIG. 30. InFIGS. 32(a) to 32(c), FIG. 32(a) shows a passing characteristic, FIG.32(b) shows an amplitude balance-characteristic in a pass band (from 925up to 960 MHz), and FIG. 32(c) shows a phase balance-characteristic in apass band. From FIG. 32, it is found that the amplitudebalance-characteristic greatly deteriorates from −0.67 dB to +0.77 dBand the phase balance-characteristic greatly deteriorates from −6.3° to+9.4° in each pass band.

In this case, the amplitude balance-characteristic denotes thedifference between the signal amplitude of the input terminal IN andoutput terminal OUT1 and the signal amplitude of the input terminal INand output terminal OUT2. When the difference becomes zero, thebalance-characteristic does not deteriorate. Moreover, the phasebalance-characteristic denotes a shift of the difference between thesignal phase of the input terminal IN and output terminal OUT1 and thesignal phase of the input terminal IN and output terminal OUT2 from180°. When the difference becomes zero, the balance-characteristic doesnot deteriorate.

However, the above-described balanced high-frequency device and thesurface acoustic wave filter described as an example of the device havea problem that the balance-characteristic which is one of importantelectrical characteristics is greatly deteriorated.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a balancedhigh-frequency device having a preferable balance-characteristic, abalanced high-frequency circuit, a phase circuit, and abalance-characteristic improving method by considering a deteriorationcause about the balanced high-frequency device and thereby deriving abalance-characteristic improving method.

To achieve the above object, a first present invention is a balancedhigh-frequency device comprising:

-   -   a balanced element;    -   at least one balanced terminal connected to the balanced        element;    -   a phase shift circuit having at least first, second, and third        impedance elements, and electrically connected between the        balanced element and the balanced terminals; wherein    -   the first impedance element and the second impedance element are        connected between the balanced terminals in series,    -   the connection point between the first impedance element and the        second impedance element is grounded through the third impedance        element,    -   a series resonant circuit is formed by the first impedance        element and the third impedance element,    -   a series resonant circuit is formed by the second impedance        element and the third impedance element, and    -   an impedance to a differential signal component in the passing        band of the balanced element of the first and second impedance        elements is set so as to increase to the ground plane.

A second present invention is the balanced high-frequency deviceaccording to the first present invention, wherein

-   -   the first and second impedance elements are capacitors, and    -   the third impedance element is an inductor.

A third present invention is the balanced high-frequency deviceaccording to the first present invention, wherein

-   -   the first and second impedance elements are inductors, and    -   the third impedance element is a capacitor.

A fourth present invention is the balanced high-frequency deviceaccording to the first present invention, wherein

-   -   an impedance in the passing band of the balanced element of the        first and second impedance elements is set so that a value        normalized by the characteristic impedance value of either of        the balanced terminals becomes 3 or more.

A fifth present invention is the balanced high-frequency deviceaccording to the first present invention, wherein

-   -   an impedance in the passing band of the balanced element of the        first and second impedance elements is set so that a value        normalized by the characteristic impedance value of either of        the balanced terminals becomes 50 or less.

A sixth present invention is the balanced high-frequency deviceaccording to the first present invention, wherein

-   -   an impedance in the passing band of the balanced elements of the        first and second impedance elements is set so that a value        normalized by the characteristic impedance value of either of        the balanced terminals ranges between 3 and 50.

A seventh present invention is the balanced high-frequency deviceaccording to any one of the first to the sixth present inventions,wherein

-   -   the balanced elements are surface acoustic wave filters,    -   the surface acoustic wave filters respectively have a        piezoelectric substrate and IDT electrodes serving as a        plurality of inter-digital transducer electrodes formed on the        piezoelectric substrate, and    -   at least one of the IDT electrodes is connected to a balanced        input terminal or balanced output terminal.

An eighth present invention is the balanced high-frequency deviceaccording to the seventh present invention, wherein

-   -   each of the surface acoustic wave filters is a longitudinal-mode        surface acoustic wave filter in which at least first, second,        and third IDT electrodes are arranged along the propagation        direction of a surface acoustic wave,    -   the second and third IDT electrodes are arranged at both sides        of the first IDT electrode,    -   the first IDT electrode is the balanced type, and    -   one and an other electrode fingers constituting the first IDT        electrode are connected to balanced input terminals or balanced        output terminals.

A ninth present invention is the balanced high-frequency deviceaccording to the seventh present invention, wherein

-   -   the surface acoustic wave filters are longitudinal-mode surface        acoustic wave filters in which at least first, second, and third        IDT electrodes are arranged along the propagation direction of a        surface acoustic wave,    -   the second and third IDT electrodes are arranged at both sides        of the first IDT electrode,    -   the fist IDT electrode is constituted of a plurality of split        IDT electrodes, and    -   at least two of the split IDT electrodes are connected to a        balanced input terminals or balanced output terminals.

A tenth present invention is the balanced high-frequency deviceaccording to the seventh present invention, wherein

-   -   the surface acoustic wave filters are longitudinal-mode surface        acoustic wave filters in which at least first, second, and third        IDT electrodes are arranged along the propagation direction of a        surface acoustic wave,    -   the second and third IDT electrodes are arranged at both sides        of the first IDT electrode,    -   the second IDT electrode is connected to either of balanced        input terminals or either of balanced output terminals, and    -   the third IDT electrode is connected to the other of the        balanced input terminals or the other of the balanced output        terminals.

An eleventh present invention is the balanced high-frequency filteraccording to any one of the first to the sixth present inventions,wherein

-   -   the balanced element is constituted of a filter using a FBAR.

A twelfth present invention is a balanced high-frequency circuit havingthe balanced high-frequency device according to any one of the first tosixth present inventions.

A thirteenth present invention is the balanced high-frequency circuitaccording to the twelfth present invention, wherein

-   -   the balanced high-frequency device of claim 7 is used for a        transmitting filter and/or receiving filter constituting the        balanced high-frequency circuit.

A fourteenth present invention is the balanced high-frequency circuitaccording to the twelfth present invention, wherein

-   -   the balance high-frequency device of the eleventh present        invention is used for a transmitting filter and/or receiving        filter constituting the balanced high-frequency circuit.

A fifteenth present invention is a balanced high-frequency circuitcomprising:

-   -   a circuit board; and    -   balanced transmission lines on the circuit board, wherein    -   the phase shift circuit of any one of the first to the sixth        present inventions is connected between the balanced lines.

A sixteenth present invention is a phase shift circuit to be connectedbetween balanced terminals or balanced lines, comprising:

-   -   at least first, second, and third impedances; wherein    -   the first impedance element and the second impedance element are        connected between the balanced terminals or balanced lines in        series,    -   the connection point between the first impedance element and the        second impedance element is grounded through the third impedance        element,    -   a series resonant circuit is formed of the first impedance        element and the third impedance element,    -   a series resonant circuit is formed of the second impedance        element and the third impedance element, and    -   an impedance to a differential signal component in the passing        band of the balanced elements of the first and second impedance        elements is set so as to increase to the ground plane.

A seventeenth present invention is the phase shift circuit according tothe sixteenth present invention, wherein

-   -   an impedance in a desired passing band of the first and second        impedance elements is set so that a value normalized by a        characteristic impedance value of either of the balanced        terminals becomes 3 or more.

An eighteenth present invention is the phase shift circuit according tothe sixteenth present invention, wherein

-   -   an impedance in a desired passing band of the first and second        impedance elements is set so that a value normalized by a        characteristic impedance value of either of the balanced        terminals becomes 50 or less.

A nineteenth present invention is the phase shift circuit according tothe sixteenth present invention, wherein

-   -   an impedance in a desired passing band of the first and second        impedance elements is set so that a value normalized by a        characteristic impedance value of either of the balanced        terminals ranges between 3 and 50.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a balanced high-frequency device in theembodiment 1 of the present invention.

FIG. 2 is an illustration for explaining the analysis of abalance-characteristic deterioration cause of a conventional surfaceacoustic wave filter.

FIGS. 3(a) and 3(b) are characteristic diagrams of thebalance-characteristic analysis of a conventional surface acoustic wavefilter, in which FIG. 3(a) is an amplitude balance-characteristicdiagram and FIG. 3(b) is a phase balance-characteristic diagram.

FIG. 4 is an illustration for explaining operations of the balancedhigh-frequency device in the embodiment 1 of the present invention.

FIG. 5 is a block diagram of the balanced high-frequency device in theembodiment 2 of the present invention.

FIG. 6 is a block diagram of the balanced high-frequency device in theembodiment 3 of the present invention.

FIGS. 7(a) to 7(c) are illustrations for explaining operations of thebalanced high-frequency device in the embodiment 3 of the presentinvention.

FIG. 8 is a block diagram of the balanced high-frequency device in theembodiment 4 of the present invention.

FIG. 9(a) is an illustration for explaining operations of the balancedhigh-frequency device in the embodiment 4 of the present invention, FIG.9(b) is an illustration showing an equivalent circuit of a phase circuiton differential-mode signal components in the embodiment 4 of thepresent invention, and FIG. 9(c) is an illustration showing anequivalent circuit of a phase circuit on common-mode signal componentsin the embodiment 4 of the present invention.

FIG. 10(a) is an illustration for explaining operations of the balancedhigh-frequency device in the embodiment 4 of the present invention, FIG.10(b) is an illustration showing an equivalent circuit of a phasecircuit on differential-mode signal components in the embodiment 4 ofthe present invention, and FIG. 10(c) is an illustration showing anequivalent circuit of a phase circuit on common-mode signal componentsin the embodiment 4 of the present invention.

FIG. 11 is a block diagram of the balanced high-frequency device in theembodiment 5 of the present invention.

FIG. 12(a) is an illustration for explaining operations of the balancedhigh-frequency device in the embodiment 5 of the present invention, FIG.12(b) is an illustration showing an equivalent circuit of a phasecircuit on differential-mode signal components in the embodiment 5 ofthe present invention, and FIG. 12(c) is an illustration showing anequivalent circuit of a phase circuit on common-mode signal componentsin the embodiment 5 of the present invention.

FIG. 13(a) is an illustration for explaining operations of the balancedhigh-frequency device in the embodiment 5 of the present invention, FIG.13(b) is an illustration showing an equivalent circuit of a phasecircuit on differential mode signal components in the embodiment 5 ofthe present invention, and FIG. 13(c) is an illustration showing anequivalent circuit of a phase circuit on common-mode signal componentsin the embodiment 5 of the present invention.

FIG. 14 is a block diagram of the balanced high-frequency device in theembodiment 6 of the present invention.

FIG. 15(a) is a passing characteristic diagram of a balancedhigh-frequency device when using the phase circuit 603, FIG. 15(b) is anamplitude balance-characteristic diagram of a balanced high-frequencydevice when using the phase circuit 603, and FIG. 15(c) is a phasebalance-characteristic diagram of a balanced high-frequency device whenusing the phase circuit 603.

FIG. 16(a) is an amplitude balance-characteristic diagram of a balancedhigh-frequency device when using the phase circuit 603 and FIG. 16(b) isa phase balance-characteristic diagram of a balanced high-frequencydevice when using the phase circuit 603.

FIG. 17(a) is a passing characteristic diagram of a balancedhigh-frequency device when using the phase circuit 901, FIG. 17(b) is anamplitude balance-characteristic diagram of a balanced high-frequencydevice when using the phase circuit 901, and FIG. 17(c) is a phasebalance-characteristic diagram of a balanced high-frequency device whenusing the phase circuit 901.

FIG. 18(a) is an amplitude balance-characteristic diagram of a balancedhigh-frequency device when using the phase circuit 901 and FIG. 18(b) isa phase balance-characteristic diagram of a balanced high-frequencydevice when using the phase circuit 901.

FIG. 19(a) is a passing characteristic diagram of a balancedhigh-frequency device when using the phase circuit 1001, FIG. 19(b) isan amplitude balance-characteristic diagram of a balanced high-frequencydevice when using the phase circuit 1001, and FIG. 19(c) is a phasebalance-characteristic diagram of a balanced high-frequency device whenusing the phase circuit 1001.

FIG. 20(a) is an amplitude balance-characteristic diagram of a balancedhigh-frequency device when using the phase circuit 1001 and FIG. 20(b)is a phase balance-characteristic diagram of a balanced high-frequencydevice when using the phase circuit 1001.

FIG. 21(a) is an impedance characteristic diagram when using the phasecircuit 601 and FIG. 21(b) is an impedance characteristic diagram whenusing the phase circuit 2201.

FIG. 22 is a block diagram in which a matching circuit is included in aphase circuit.

FIG. 23(a) is a block diagram of a balanced high-frequency device in theembodiment 7 of the present invention and FIG. 23(b) is a block diagramof a balanced high-frequency device having a phase circuit including amatching circuit.

FIG. 24 is a block diagram of a balanced high-frequency device in theembodiment 8 of the present invention.

FIG. 25 is a block diagram of a balanced high-frequency device in theembodiment 9 of the present invention.

FIG. 26 is a block diagram of a balanced high-frequency device in theembodiment 10 of the present invention.

FIG. 27 is a block diagram of a balanced high-frequency circuit in theembodiment 11 of the present invention.

FIG. 28 is a block diagram of a conventional balanced high-frequencydevice.

FIG. 29(a) and 29(b) are block diagrams including a matching circuit ofa conventional balanced high-frequency device, in which FIG. 29(a) is ablock diagram when the matching circuit is constituted by one impedanceelement and FIG. 29(b) is a block diagram when the matching circuit isconstituted by two impedance elements.

FIG. 30 is a block diagram of a conventional surface acoustic wavefilter.

FIG. 31 is a block diagram including a matching circuit of aconventional surface acoustic wave filter.

FIG. 32(a) is a passing characteristic diagram of a conventional surfaceacoustic wave filter, FIG. 32(b) is an amplitude characteristic diagramof a conventional surface acoustic wave filter, and FIG. 32(c) is aphase balance-characteristic diagram of a conventional surface acousticwave filter.

FIG. 33(a) is a passing characteristic diagram of a balancedhigh-frequency device when using a phase circuit 1201;

FIG. 33(b) is an amplitude balance characteristic diagram of a balancedhigh-frequency device when using the phase circuit 1201;

FIG. 33(c) is a phase balance characteristic diagram of a balancedhigh-frequency device when using the phase circuit 1201;

FIG. 34(a) is an illustration showing a relation between amplitudebalance characteristic and normalized impedance of a balancedhigh-frequency device when using the phase circuit 1201;

FIG. 34(b) is an illustration showing a relation between amplitudebalance characteristic and normalized impedance of a balancedhigh-frequency device when using the phase circuit 1201;

FIG. 35 is an illustration showing a relation between loss andnormalized impedance of a balanced high-frequency device when using thephase circuit 1201;

FIG. 36(a) is a passing characteristic diagram of a balancedhigh-frequency device when using a phase circuit 1301;

FIG. 36(b) is an amplitude balance characteristic diagram of a balancedhigh-frequency device when using the phase circuit 1301;

FIG. 36(c) is a phase balance characteristic diagram of a balancedhigh-frequency device when using the phase circuit 1301;

FIG. 37(a) is an illustration showing a relation between amplitudebalance characteristic and normalized impedance of a balancedhigh-frequency device when using the phase circuit 1301;

FIG. 37(b) is an illustration showing a relation between amplitudebalance characteristic and normalized impedance of a balancedhigh-frequency device when using the phase circuit 1301;

FIG. 38 is an illustration showing a relation between loss andnormalized impedance of a balanced high-frequency device when using thephase circuit 1301; and

FIG. 39 is a block diagram of an FBAR.

DESCRIPTION OF SYMBOLS

-   101 Balanced high-frequency device-   102 Balanced device-   103 Phase circuit-   201 Surface acoustic wave filter-   202 Ideal surface acoustic wave filter-   203, 204 Capacity component-   501 Balanced high-frequency device-   502 Balanced device-   503, 504 Phase circuit-   601 Balanced high-frequency device-   602 Balanced device-   603 Phase circuit-   604 Transmission line-   801 Balanced high-frequency device-   802 Balanced device-   803 Phase circuit-   804, 805, 806 Impedance element-   901 Phase circuit-   902, 903 Capacitor-   904 Inductor-   905 Virtual ground point-   1001 Phase circuit-   1002, 1003 Capacitor-   1004 Capacitor-   1005 Virtual ground point-   1101 Balanced high-frequency device-   1102 Balanced device-   1103 Phase circuit-   1104, 1105, 1106 Impedance element-   1201 Phase circuit-   1202, 1203 Inductor-   1204 Capacitor-   1205 Connection point-   1301 Phase circuit-   1302, 1303 Capacitor-   1304 Inductor-   1305 Connection point-   1401 Balanced high-frequency device-   1402 Surface acoustic wave filter-   1403 Phase circuit-   1404 Piezoelectric substrate-   1405 First IDT electrode-   1406 Second IDT electrode-   1407 Third IDT electrode-   1408 First reflector electrode-   1409 Second reflector electrode-   1601, 1801, 2001 Maximum value of amplitude balance-characteristic    deterioration of conventional surface acoustic wave filter-   1602, 1802, 2002 Minimum value of amplitude balance-characteristic    deterioration of conventional surface acoustic wave filter-   1603, 1803, 2003 Maximum value of phase balance-characteristic    deterioration of conventional surface acoustic wave filter-   1604, 1804, 2004 Minimum value of phase balance-characteristic    deterioration of conventional surface acoustic wave filter-   2101, 2102 Region showing vicinity of band pass frequency-   2201 Phase circuit-   2202 Capacitor-   2301 Balanced high-frequency device-   2302 Phase circuit-   2304, 2305 Capacitor-   2306 Inductor-   2307 Inductor serving as matching circuit-   2308 Virtual ground point-   2309 Combined inductor-   2401 Balanced high-frequency device-   2402 Surface acoustic wave filter-   2403 Phase circuit-   2404 Piezoelectric substrate-   2405 First IDT electrode-   2406 Second IDT electrode-   2407 Third IDT electrode-   2408 First reflector electrode-   2409 Second reflector electrode-   2410 First divided IDT electrode-   2411 Second divided IDT electrode-   2501 Balanced high-frequency device-   2502 Surface acoustic wave filter-   2503 Phase circuit-   2504 Piezoelectric substrate-   2505 First IDT electrode-   2506 Second IDT electrode-   2507 Third IDT electrode-   2508 First reflector electrode-   2509 Second reflector electrode-   2601 Balanced high-frequency device-   2602 Semiconductor device-   2603 Phase circuit-   2604 a, 2604 b, 2605 a, 2605 b Bipolar transistor-   2606 a, 2606 b Inductor-   2607 DC-cut capacitor-   2608 Bypass capacitor-   2609 a, 2609 b DC-cut capacitor-   2610, 2611 Bias circuit-   2612 a, 2612 b Choke inductor-   2701 Balanced high-frequency circuit-   2702 Transmitting amplifier-   2703 Transmitting filter-   2704 Switch-   2705 Antenna-   2706 Receiving filter-   2707 Receiving amplifier-   2708, 2709 Balanced transmission line-   2801, 2901 Balanced high-frequency device-   2902, 2904, 2905 Matching circuit-   2903 Balanced high-frequency device-   3001 Surface acoustic wave filter-   3002 Piezoelectric substrate-   3003 First IDT electrode-   3004 Second IDT electrode-   3005 Third IDT electrode-   3006 First reflector electrode-   3007 Second reflector electrode-   3101 Surface acoustic wave filter-   3102 Piezoelectric substrate-   3103 First IDT electrode-   3104 Second IDT electrode-   3105 Third IDT electrode-   3106 First reflector electrode-   3107 Second reflector electrode-   3108 First divided IDT electrode-   3109 Second divided IDT electrode-   3110 Inductor-   3401, 3701 Maximum value of amplitude balance characteristic    deterioration of conventional surface acoustic wave filter-   3402, 3702 Minimum value of amplitude balance characteristic    deterioration of conventional surface acoustic wave-   3403, 3703 Maximum value of phase balance characteristic    deterioration of conventional surface acoustic wave filer-   3404, 3704 Minimum value of phase balance characteristic    deterioration of conventional surface acoustic wave filter

PREFERRED EMBODIMENTS OF THE INVENTION

Embodiments of the present invention are described below by referring tothe accompanying drawings.

Embodiment 1

A balanced high-frequency device of embodiment 1 of the presentinvention is described below by referring to the accompanying drawings.FIG. 1 shows a configuration of a balanced high-frequency device 101 ofthe embodiment 1 of the present invention. In FIG. 1, the balancedhigh-frequency device 101 is constituted by a balanced device 102 and aphase circuit 103. Moreover, in the case of a balanced device 102, theinput-side terminal is an input terminal IN serving as an unbalancedinput/output terminal and the output-side terminals are output terminalsOUT1 and OUT2 serving as balanced input/output terminals. Furthermore, aphase circuit 103 is connected between the output terminals. By usingthe above configuration, it is possible to realize a balancedhigh-frequency device having an unbalanced-balanced input/outputterminal.

First, a balance-characteristic deterioration cause of the balancedhigh-frequency device is studied by using an surface acoustic wavefilter. The conventional surface acoustic wave filter 201 shown in FIG.30 has a problem that a balance-characteristic deteriorates. In thiscase, the balance-characteristic is analyzed by the configuration shownin FIG. 2. In FIG. 2, the surface acoustic wave filter 201 isconstituted by an ideal surface acoustic wave filter 202 whosebalance-characteristic is not deteriorated and capacitive components 203and 204. Combination by the parasitic component of the surface acousticwave filter 201 is assumed by connecting the capacitive components 203and 204 between the input side and output side of the ideal surfaceacoustic wave filter 202.

FIGS. 3(a) and 3(b) show filter characteristics when setting thesecapacitive components 203 and 204 to substantially 0.1 pF in which FIG.3(a) shows an amplitude balance-characteristic in a pass band and FIG.3(b) shows a phase balance-characteristic in a pass band. A result ofanalyzing the balance-characteristic in FIG. 3 very well coincides withthe measured characteristic of the conventional surface acoustic wavefilter shown in FIG. 32 as a trend of balance-characteristicdeterioration. Therefore, combination of the input terminal and outputterminal of a balanced device is considered as a main factor ofbalance-characteristic deterioration.

Operations of the balanced high-frequency device of the embodiment 1 ofthe present invention are described below by referring to theaccompanying drawings. FIG. 4 shows the outline of operations of thebalanced high-frequency device 101 of the embodiment 1 of the presentinvention. Combination due to a parasitic component between an inputterminal and an output terminal is estimated as a main factor ofdeterioration of the balance-characteristic of the balancedhigh-frequency device 101. It is considered that the above mentioned canbe explained by showing a signal component flowing through balancedinput and output terminals by an common-mode signal component and adifferential-mode signal component. Here, common-mode signal componentmeans common-mode signal component, and differential-mode signalcomponent means opposite-phase signal component. That is, a signalcomponent i input from the input terminal IN is differentially output asdifferential-mode signal components id1 and id2 by the balanced device102. However, the combination by a parasitic component is not madedifferential by the output terminal OUT1 or OUT2 but it is superimposedas common-mode signal components ic1 and ic2 and the common-mode signalcomponents ic1 and ic2 cause the balance-characteristic to deteriorate.

Therefore, in the case of an embodiment of the present invention, it ispossible to reduce the common-mode components ic1 and ic2 when the phasecircuit 103 operates as a resonant circuit at a predetermined frequencyto make impedances of the common-mode signal components ic1 and ic2 whenviewing the output-terminal side from the balanced device 102 lower thanimpedances of the differential-mode signal components id1 and id2 whenviewing the output-terminal side from the balanced device 102.

As described above, the balanced high-frequency device 101 of thepresent invention realizes a balanced high-frequency device excellent inbalance-characteristic by reducing the common-mode signal components ic1and ic2 by the phase circuit 103.

In the case of this embodiment, it is described that the input-sideterminal is an input terminal IN serving as an unbalanced input/outputterminal, the output-side terminals are output terminals OUT1 and OUT2serving as balanced input/output terminals, and the phase circuit 103 isconnected between the output terminals. However, this embodiment is notrestricted to the above case. It is also allowed that the input-sideterminal is an input terminal serving as a balanced input/outputterminal, the output-side terminal is an output terminal serving as anunbalanced input/output terminal, and the phase circuit 103 is connectedbetween input terminals.

Embodiment 2

A balanced high-frequency device of embodiment 2 of the presentinvention is described below by referring to the accompanying drawings.FIG. 5 shows a configuration of a balanced high-frequency device 501 ofthe embodiment 2 of the present invention. In FIG. 5, the balancedhigh-frequency device 501 is constituted by a balanced device 502 andphase circuits 503 and 504. Moreover, in the case of the balanced device502, the input-side terminal is an input terminal IN serving as abalanced input/output terminal and the output-side terminals are outputterminals OUT1 and OUT2 serving as balanced input/output terminals. Byusing the above configuration, it is possible to realize a balancedhigh-frequency device having balanced-unbalanced input and outputterminals.

Also in the case of the balanced high-frequency device 501 of thepresent invention, it is possible to realize a balanced high-frequencydevice excellent in balance-characteristic because the phase circuit 503operates as a resonant circuit at a predetermined frequency and makesimpedances of common-mode signal components ic1 and ic2 when viewing theinput-terminal side from the balanced device 502 lower than those ofdifferential-mode signal components id1 and id2 when viewing theinput-terminal side from the balanced device 502 and the phase circuit504 operates as a resonant circuit at a predetermined frequency andmakes impedances of the common-mode signal components ic1 and ic2 whenviewing the output-terminal side from the balanced device 502 lower thanthose of the differential-mode signal components id1 and id2 whenviewing the output-terminal side from the balanced device 502 andthereby, reduces the common-mode signal components ic1 and ic2.

Embodiment 3

A balanced high-frequency device of embodiment 3 of the presentinvention is described below by referring to the accompanying drawings.A more specific circuit configuration is shown below as a phase circuit.FIG. 6 shows a configuration of a balanced high-frequency device 601 ofthe embodiment 2 of the present invention. In FIG. 6, the balancedhigh-frequency device 601 is constituted by a balanced device 602 and aphase circuit 603. Moreover, in the case of the balanced device 602, theinput-side terminal is an input terminal IN serving as an unbalancedinput/output terminal and output-side terminals are output terminalsOUT1 and OUT2 serving as balanced input/output terminals. Furthermore,the phase circuit 603 is constituted by a transmission line 604 and setbetween output terminals. The transmission line 604 has a length of λ/2(in this case, λ denotes a wavelength) which corresponds to a phaseshift of 180°. Furthermore, in this case, λ is equal to a frequency in apass band or nearby the pass band. By using the above configuration, itis possible to realize a balanced high-frequency device having anunbalanced-balanced input/output terminal.

Operations of the balanced high-frequency device 601 are described byreferring to the accompanying drawings. As shown in FIG. 7(a), when asignal component i is input to the balanced device 602 from the inputterminal IN, common-mode signal components ic1 and ic2 anddifferential-mode signal components id1 and id2 are output from thebalanced device. A transmission line 604 set between output terminalsperforms operations different from each other for the common-mode signalcomponents ic1 and ic2 and differential-mode signal components id1 andid2. That is, as shown in FIG. 7(b), for the common-mode signalcomponents ic1 and ic2, a configuration is realized in which a openedλ/4 line is connected to the output terminals OUT1 and OUT2 respectivelyand operates as a series resonant circuit, impedances of the outputterminals to a ground plane almost becomes short, and the common-modesignal component ic1 or ic2 is not propagated to the output terminalOUT1 or OUT2.

Moreover, for the differential-mode signal components id1 and id2, aconfiguration is realized in which shorted λ/4 line is connected to theoutput terminals OUT1 and OUT2 respectively because a virtual settingplane is formed at the middle point of the transmission line 604,operates as a parallel resonant circuit, and impedances of the outputterminals to ground planes almost become open, and thereby thedifferential-mode signal components id1 and id2 are propagated to theoutput terminals OUT1 and OUT2.

As described above, the balanced high-frequency device of the embodiment3 of the present invention makes it possible to reduce common-modesignal components by using the transmission line 604 as a phase circuitand thus, it is possible to realize a balanced high-frequency deviceexcellent in balance-characteristic.

In the case of this embodiment, the phase circuit is constituted by thetransmission line. However, the configuration of the phase circuit isnot restricted to the above configuration. By using a configurationoperating as a phase circuit, the same advantage as the presentinvention can be obtained.

Moreover, it is allowed that a phase circuit is formed on a circuitsubstrate by using a transmission line and a chip component orintegrated on a substrate with a balanced device mounted or in apackage. Furthermore, it is allowed to form a part of the phase circuitin a laminated device constituted by forming electrode patterns on aplurality of dielectric layers and laminating the dielectric layers.Furthermore, by constituting the laminated device so as to have anothercircuit function and integrating the laminated device with a balancedhigh-frequency device of the present invention as a composite device, itis possible to realize a multifunctional compact balanced high-frequencydevice.

In the case of this embodiment, an input terminal is described as theunbalanced type and an output terminal is described as the balancedtype. However, it is allowed that an input terminal is the balanced typeand an output terminal is the unbalanced type. Moreover, it is allowedthat both input terminal and output terminal are the balanced type.

Embodiment 4

A balanced high-frequency device of embodiment 4 of the presentinvention is described below by referring to the accompanying drawings.A more specific circuit configuration is shown below as a phase circuit.FIG. 8 shows a configuration of a balanced high-frequency device of theembodiment 4 of the present invention. In FIG. 8, the balancedhigh-frequency device 801 is constituted by a balanced device 802 and aphase circuit 803. In the case of the balanced device 802, theinput-side terminal is an input terminal IN serving as an unbalancedinput/output terminal and output-side terminals are output terminalsOUT1 and OUT2 serving as balanced input/output terminals.

The phase circuit 803 is constituted by impedance elements 804, 805, and806. In this case, the output terminals OUT1 and OUT2 are groundedthrough impedance elements 804 and 805, the impedance element 806 isconnected between the output terminals, and the phase circuit 803 isalso connected between the output terminals. In this case, the impedanceelements 804 and 805 substantially have the same impedance and theimaginary part of the impedance of the impedance element 806 is reverseto that of the impedances of the impedance elements 804 and 805 inpolarity. By using the above configuration, a balanced high-frequencydevice having unbalanced-balanced input and output terminals can beobtained.

Then, operations of the balanced high-frequency device of the embodiment4 of the present invention are described below by using a specificimpedance element. FIGS. 9(a) and 9(b) are illustrations for explainingoperations of the balanced high-frequency device of the embodiment 4 ofthe present invention. As shown in FIG. 9(a), a phase circuit 901 isconstituted by capacitors 902 and 903 and an inductor 904. As shown inFIG. 9(a), when a signal component i is input to the balanced device 802from the input terminal IN, common-mode signal components ic1 and ic2and differential-mode signal components id1 and id2 are output from thebalanced device. In this case, the inductor 904 connected between outputterminals forms a virtual ground point 905 on the differential-modesignal components id1 and id2.

FIG. 9(b) shows the equivalent circuit of the phase circuit 901 on thedifferential-mode signal components id1 and id2. Because the inductor904 forms the virtual ground point 905 on the differential-mode signalcomponents id1 and id2, the capacitor 902 and a part of the inductor 904form a parallel resonant circuit to a ground plane at the outputterminal OUT1 and the capacitor 903 and apart of the inductor 904 form aparallel resonant circuit to a ground plane at the output terminal OUT2.By designing parallel resonant frequencies of the parallel resonantcircuits so as to be kept in a pass band or nearby the pass band,impedances of the differential-mode signal components id1 and id2 at apredetermined frequency to a ground plane approach infinity andtransferred to the output terminals without being shorted to a groundplane. That is, on the differential-mode signal components, operationssubstantially same as those shown in FIG. 7(c) are executed. FIG. 9(c)shows the equivalent circuit of the phase circuit 901 on the common-modesignal components ic1 and ic2. OUT1 and OUT2 have almost equalpotentials on the common-mode signal components, the inductance 904 doesnot form a virtual ground point on the common-mode signal components ic1and ic2, and OUT1 and OUT2 are substantially open. In this case, a partof the inductor 904 denotes a range up to the virtual ground point 905{refer to FIG. 9(b)}.

Thus, by designing impedances of the capacitors 902 and 903 serving asimpedance elements arranged between the balanced input/output terminalsOUT1 and OUT2 and ground planes to sufficiently small values, thecommon-mode signal components ic1 and ic2 are shorted to ground planesand therefore, they are not transferred to the balanced input/outputterminals.

Moreover, it is allowed that the phase circuit of the embodiment 4 ofthe present invention has the configuration shown in FIG. 10. FIGS.10(a) to 10(c) are illustrations for explaining operations of thebalanced high-frequency device of the embodiment 4 of the presentinvention. As shown in FIG. 10(a), a phase circuit 1001 is constitutedby inductors 1002 and 1003 and a capacitor 1004. As shown in FIG. 10(a),when a signal component i is input to a balanced device 802 from aninput terminal IN, common-mode signal components ic1 and ic2 anddifferential-mode signal components id1 and id2 are output from thebalanced device. In this case, the capacitor 1004 connected betweenoutput terminals forms a virtual ground point 1005 on differential-modesignal components id1 and id2.

FIG. 10(b) shows the equivalent circuit of the phase circuit 1001 on thedifferential-mode signal components id1 and id2. As shown in FIG. 10(b),because the capacitor 1004 forms a virtual ground point 1005 on thedifferential-mode signal components id1 and id2, the inductor 1002 and apart of the capacitor 1004 form a parallel resonant circuit to a groundplane at the output terminal OUT1 and the inductor 1003 and a part ofthe capacitor 1004 form a parallel resonant circuit to aground plane atthe output terminal OUT2. Therefore, by designing parallel resonantfrequencies of the parallel resonant circuits so that they are kept in apass band or nearby the pass band, impedances of the differential-modesignal components id1 and id2 at desired frequencies to a ground planeapproach infinity and the components are transferred to the outputterminals without being shorted to ground planes. That is, operationssubstantially same as those shown in FIG. 7(c) are executed on thedifferential-mode signal components id1 and id2. FIG. 10(c) shows theequivalent circuit of the phase circuit 1001 on the common-mode signalcomponents ic1 and ic2. OUT1 and OUT2 have almost equal potential on thecommon-mode signal components, the capacitor 1004 does not form avirtual ground point on the common-mode signal component ic1 or ic2, andOUT1 and OUT2 substantially become open. In this case, a part of thecapacitor 1004 denotes a range up to the virtual ground point (refer toFIG. 10(b)).

Therefore, by designing impedances of the inductors 1002 and 1003serving as impedance elements arranged between the balanced input/outputterminals OUT1 and OUT2 and ground planes to sufficiently small values,the common-mode signal components ic1 and ic2 are shorted to groundplanes and therefore, they are not transferred to the balanced inputterminals.

As described above, in the case of the balanced high-frequency device ofthe embodiment 4 of the present invention, it is possible to reducecommon-mode signal components by using three impedance elements as phasecircuits and thus, realize a balanced high-frequency device excellent inbalance-characteristic.

In the case of this embodiment, the numbers of and configurations ofinductors and capacitors serving as impedance elements constituting aphase circuit are not restricted to the above case. Moreover, thoughdevice values of the impedance elements 804 and 805 are substantiallyequal to each other, it is not always necessary that they are equal toeach other. They are optimally selected in accordance with a circuitconfiguration. By using a configuration operating as a phase circuit,the same advantage as the present invention can be obtained.

Moreover, it is allowed that a phase circuit is formed on a circuitsubstrate by using a transmission line and a chip component orintegrated on a substrate with a balanced device mounted or in apackage. Furthermore, it is allowed to form a part of the phase circuitin a laminated device constituted by forming electrode patterns on aplurality of dielectric layers and laminating the dielectric layers.Furthermore, by constituting the laminated device so as to have anothercircuit function and integrating the laminated device with a balancedhigh-frequency device of the present invention as a composite device, itis possible to realize a multifunctional compact balanced high-frequencydevice.

Furthermore, in the case of this embodiment, it is described that aninput terminal is the unbalanced type and an output terminal is thebalanced type. However, it is allowed that the input terminal is thebalanced type and the output terminal is the unbalanced type.Furthermore, it is allowed that both the input terminal and outputterminal are the balanced type.

Embodiment 5

A balanced high-frequency device of embodiment 5 of the presentinvention is described below by referring to the accompanying drawings.A more specific circuit configuration is shown below as a phase circuit.FIG. 11 shows a configuration of a balanced high-frequency device 1101of the embodiment 5 of the present invention. In FIG. 11, the balancedhigh-frequency device 1101 is constituted by a balanced device 1102 anda phase circuit 1103. Moreover, in the case of the balanced device 1102,the input-side terminal is an input terminal IN serving as an unbalancedinput/output terminal and output-side terminals are output terminalsOUT1 and OUT2 serving as balanced terminals.

The phase circuit 1103 is constituted by impedance elements 1104, 1105,and 1106. The impedance elements 1104 and 1105 are connected between theoutput terminals in series and the middle point 1107 between theimpedance elements 1104 and 1105 is grounded through the impedanceelement 1106 and the phase circuit 1103 is connected between the outputterminals. In this case, the imaginary part of the impedance of theimpedance element 1106 is opposite to imaginary parts of impedances ofthe impedance elements 1104 and 1105 in polarity. Moreover, theimpedance elements 1104 and 1105 have the substantially same value. Byusing the above configuration, it is possible to obtain a balancedhigh-frequency device having an unbalanced-balanced input/outputterminal.

Then, operations of a balanced high-frequency device of the presentinvention are described below by using a specific impedance element.FIGS. 12(a) to 12(c) are illustrations for explaining operations of thebalanced high-frequency device of the present invention. As shown inFIG. 12(a), a phase circuit 1201 is constituted by inductors 1202 and1203 and a capacitor 1204. As shown in FIG. 12(a), when a signalcomponent i is input from an input terminal IN to the balanced device1102, common-mode signal components ic1 and ic2 and differential-modesignal components id1 and id2 are output from the balanced device 1102.FIG. 12(b) shows the equivalent circuit of the phase circuit 1201 on thedifferential-mode signal components. As shown in FIG. 12(b), theconnection point 1205 between the inductors 1202 and 1203 serves as avirtual ground point on the differential-mode signal components id1 andid2. Therefore, by sufficiently increasing values of the inductors 1202and 1203, it is possible to increase an impedance to a ground plane andthe differential-mode signal components id1 and id2 are transferred tooutput terminals OUT1 and OUT2.

Moreover, FIG. 12(c) shows the equivalent circuit of the phase circuit1201 on common-mode signal components. As shown in FIG. 12(c), theconnection point 1205 between the inductors 1202 and 1203 does not serveas a virtual ground point on the common-mode signal components ic1 andic2. Therefore, by designing the inductor 1202 and a part of thecapacitor 1204 and the inductor 1203 and a part of the capacitor 1204 sothat they form a series resonant circuit at a predetermined frequency,common-mode signal components are shorted to ground planes andtherefore, they are not transferred to the output terminal OUT1 or OUT2.In this case, a part of the capacitor 1204 denotes one hand equivalentlybecoming parallel connection (refer to FIG. 12(c)).

Furthermore, it is allowed that a phase circuit of the present inventionhas the configuration shown in FIGS. 13(a) to 13(c). FIGS. 13(a) to13(c) are illustrations for explaining operations of the balancedhigh-frequency device of the present invention. As shown in FIG. 13(a),a phase circuit 1301 is constituted by capacitors 1302 and 1303 and aninductor 1304. As shown in FIG. 13(a), when a signal component i isinput from an input terminal IN to the balanced device 1102, common-modesignal components ic1 and ic2 and differential-mode signal componentsid1 and id2 are output from the balanced device 1102. FIG. 13(b) showsthe equivalent circuit of the phase circuit 1301 on thedifferential-mode signal components id1 and id2. As shown in FIG. 13(b),the connection point 1305 between the capacitors 1302 and 1303 serves asa virtual ground point on the differential-mode signal components id1and id2. Therefore, by sufficiently decreasing values of the capacitors1302 and 1303, it is possible to increase an impedance to a ground planeand the differential-mode signal components are transferred to theoutput terminals OUT1 and OUT2.

FIG. 13(c) shows the equivalent circuit of the phase circuit 1301 on thecommon-mode signal components ic1 and ic2. As shown in FIG. 13(c), theconnection point 1305 between the capacitors 1302 and 1303 does notserve as a virtual ground point on the common-mode signal components ic1and ic2. Therefore, by designing the capacity 1302 and a part of theinductor 1304 and the capacitor 1303 and a part of the inductor 1304 sothat they respectively form a series resonant circuit at a predeterminedfrequency, common-mode signal components are shorted to ground planesand therefore, they are not transferred to the output terminal OUT1 orOUT2. In this case, a part of the inductor 1304 denotes one handequivalently becoming parallel connection (refer to FIG. 13(c)).

As described above, the balanced high-frequency device of the embodiment5 of the present invention can reduce common-mode signal components byusing three impedance elements as phase circuits and therefore, it ispossible to realize a balanced high-frequency device excellent inbalance-characteristic.

Moreover, in the case of this embodiment, the numbers of andconfigurations of inductors and capacitors serving as impedance elementconstituting a phase circuit are not restricted to the above case.Furthermore, though devices values of the impedance elements 1104 and1105 are substantially equal to each other, it is not always necessarythat the values are equal to each other but the values are optimallyselected in accordance with a circuit configuration. Therefore, by usinga configuration operating as a phase circuit, the same advantage as thepresent invention can be obtained.

Furthermore, it is allowed that a phase circuit is formed on a circuitsubstrate by using a transmission line and a chip component or formed ona substrate with a balanced device mounted or in a substrate.Furthermore, it is allowed to form a part of the phase circuit in alaminated device constituted by forming electrode patterns on aplurality of dielectric layers and laminating the dielectric layers.Furthermore, by constituting the laminated device so as to have anothercircuit function and integrating the laminated device with a balancedhigh-frequency device of the present invention as a composite device, itis possible to realize a multifunctional compact balanced high-frequencydevice.

In the case of this embodiment, it is described that an input terminalis the unbalanced type and an output terminal is the balanced type.However, it is also allowed that the input terminal is the balanced typeand the output terminal is the unbalanced type. Furthermore, it isallowed that both the input terminal and output terminal are thebalanced type.

Embodiment 6

Then, a balanced high-frequency device of embodiment 6 of the presentinvention is described below by referring to the accompanying drawings.A specific configuration of the balanced high-frequency device isdescribed below on a case of using an surface acoustic wave filter as abalanced device. FIG. 14 shows a configuration of a balanced device ofthe present invention. In FIG. 14, a balanced high-frequency device 1401is constituted by an surface acoustic wave filter 1402 and a phasecircuit 1403 respectively serving as a balanced device. Moreover, in thecase of the surface acoustic wave filter 1402, the input-side terminalis an input terminal IN serving as an unbalanced input/output terminaland output-side terminals are output terminals OUT1 and OUT2 serving asbalanced input/output terminals. Moreover, the phase circuit 1403 isconnected between the output terminals.

The surface acoustic wave filter 1402 is constituted on a piezoelectricsubstrate 1404 by first, second, and third inter-digital transducerelectrodes (hereafter respectively referred to as IDT electrode) 1405,1406, and 1407 and first and second reflector electrodes 1408 and 1409.One-hand electrode finger of the first IDT electrode 1405 is connectedto the output terminal OUT1 and the other-hand electrode finger of thefirst IDT electrode 1405 is connected to the output terminal OUT2.Moreover, one-hand electrode fingers of the second and third IDTelectrodes 1406 and 1407 are connected to the input terminal IN and theother-hand electrode fingers of them are grounded. By using the aboveconfiguration, it is possible to obtain a balanced high-frequency devicehaving an unbalanced-balanced input/output terminal.

Then, specific characteristics of the balanced high-frequency device ofthis embodiment are described below. FIGS. 15(a) to 15(c) showcharacteristics of the balanced high-frequency device 1401 when usingthe phase circuit 603 shown in FIG. 6 as the phase circuit 1403. In thiscase, the transmission line 604 constituting the phase circuit 603 hassubstantially a length of λ/2 which corresponds to a phase shift of180°. FIG. 15(a) shows a passing characteristic, FIG. 15(b) showsamplitude balance-characteristic of a pass band, and FIG. 15(c) shows aphase balance-characteristic of a pass band. The balance-characteristicsin FIGS. 15(b) and 15(c) are greatly improved compared to conventionalcharacteristics shown in FIG. 31 and are almost close to an idealcharacteristic. Moreover, in the case of the passing characteristic, theattenuation at the high pass-band side is improved by approx. 5 dB.

Then, a case of changing the length of the transmission line 604 isevaluated. FIGS. 16(a) and 16(b) show balance-characteristics whenchanging the length of the transmission line 604. FIG. 16(a) showsamplitude balance-characteristics and FIG. 16(b) shows phasebalance-characteristics. Moreover, symbols 1601 and 1602 denote themaximum value and minimum value of deteriorations in the amplitudebalance-characteristic in a pass band of the surface acoustic wavefilter of this embodiment. Symbols 1603 and 1604 denote the maximumvalue and minimum value of deteriorations in the phasebalance-characteristics in the bass band of the surface acoustic wavefilter of this embodiment. Furthermore, broken lines show the maximumvalue and minimum value of deteriorations in the balance-characteristicsof a conventional surface acoustic wave filter. From FIGS. 16(a) and16(b), it is found that the balance-characteristics are improved whenthe transmission line length ranges substantially between λ/4 and 3λ/4.Moreover, it is found that a more preferable balance-characteristic isobtained when the amplitude balance-characteristic ranges betweensubstantially −5 dB and +5 dB and the phase balance-characteristicranges between substantially −0.5° and +0.5° by keeping a phase angle insubstantially the range between 3λ/8 and 5λ/8.

Then, characteristics when using a phase circuit of anotherconfiguration are shown. FIGS. 17(a) to 17(c) show characteristics ofthe balanced high-frequency device 1401 when using the phase circuit 901shown in FIG. 9 as the phase circuit 1403. In this case, capacitancesCg1 and Cg2 of the capacitors 902 and 903 are substantially equal toeach other so that impedances of the capacitors 902 and 903 respectivelybecome 3 Ω at the frequency in a pass band. Moreover, the inductance Lbof the inductor 904 is designed so that parallel resonant frequenciesbetween Cg1 and Lb/2 and between Cg2 and Lb/2 are kept in a pass band.

FIG. 17(a) shows a passing characteristic, FIG. 17(b) shows an amplitudebalance-characteristic of a pass band, and FIG. 17(c) shows a phasebalance-characteristic of a pass band. The balance-characteristics aregreatly improved compared to those shown in FIG. 31 and are almost closeto an ideal state. Moreover, in the case of the passing characteristics,the attenuation at the high pass-band side is improved by approx. 5 dB.

Then, a case in which impedances of the capacitors 902 and 903 arechanged is evaluated. FIGS. 18(a) and 18(b) show balance-characteristicsto standardized impedances obtained by dividing impedances of thecapacitors 902 and 903 by the characteristic impedance of a terminal. Inthis case, because the characteristic impedance of a balanced outputterminal is equal to substantially 50 Ω, it is assumed that thecharacteristic impedance of each terminal is equal to substantially 25Ω. FIG. 18(a) shows amplitude balance-characteristics and FIG. 18(b)shows phase balance-characteristics. Moreover, symbols 1801 and 1802denote the maximum value and minimum value of deteriorations in theamplitude balance-characteristics in the pass band of the surfaceacoustic wave filter of this embodiment and 1803 and 1804 denote themaximum value and minimum value of deteriorations in the phasebalance-characteristics in the pass band of the surface acoustic wavefilter of this embodiment. From FIGS. 18(a) and 18(b), it is found thatthe balance-characteristics are improved when standardized impedancesare equal to or less than 2.

Then, characteristics when using a phase circuit of anotherconfiguration are described below. FIGS. 19(a) to 19(c) showcharacteristics of the balanced high-frequency device 1401 when usingthe phase circuit 1001 shown in FIG. 10 as the phase circuit 1403. Inthis case, inductance values Lg1 and Lg2 of the inductors 1002 and 1003are substantially equal to each other and the inductors 1002 and 1003are designed so that impedances of the inductors are respectively equalto substantially 3 Ω at the frequency in a pass band. Moreover, thecapacitance Cb of the capacitor 1004 is designed so that parallelresonant frequencies between Lg1 and 2Cb and between Lg2 and 2Cb arekept in a pass band.

FIG. 19(a) shows a passing characteristic, FIG. 19(b) shows an amplitudebalance-characteristic of a pass band, and FIG. 19(c) shows a phasebalance-characteristic of a pass band. The balance-characteristics aregreatly improved compared to conventional characteristics shown in FIG.31 and are almost close to an ideal state. Moreover, in the case of thepassing characteristic, the attenuation at the high pass band side isimproved by approx. 5 dB.

Then, a case is evaluated in which impedances of the inductors 1002 and1003 are changed. FIGS. 20(a) and 20(b) show balance-characteristics tostandardized impedances obtained by dividing the impedances of theinductors 1002 and 1003 by the characteristic impedance of a terminal.In this case, because the characteristic impedance of a balanced outputterminal is substantially equal to 50 Ω, the characteristic impedance ofeach terminal is set to substantially 25 Ω. FIG. 20(a) shows amplitudebalance-characteristics and FIG. 20(b) shows phasebalance-characteristics. Moreover, symbols 2001 and 2002 denote themaximum value and minimum value of deteriorations in the amplitudebalance-characteristics in the pass band of the surface acoustic wavefilter of this embodiment and 2003 and 2004 denote the maximum value andminimum value of deteriorations in the phase balance-characteristics inthe bass band of the surface acoustic wave filter of this embodiment.

From FIG. 20, it is found that the phase balance-characteristics areimproved when the standardized impedance is substantially 2 or less.Moreover, the amplitude balance-characteristics are improved when thestandardized impedance is substantially 0.5 or less. Therefore, it ispreferable to keep the standardized impedance at substantially 2 orless. More preferably, by preferably keeping the standardized impedanceat substantially 0.5 or less, it is possible to improve thebalance-characteristics.

As described above, in the case of the balanced high-frequency device1401 of the embodiment 6 of the present invention, it is possible toreduce common-mode components by using three impedance elements as phasecircuits and thereby realize a balanced high-frequency device excellentin balance-characteristic.

Moreover, though this embodiment is described by using a transmissionline as a phase circuit, it is preferable that the transmission linesubstantially has a length of λ/2. This is because the phase circuitmore frequently operates as an inductor or capacitor as thetransmission-line length is shifted from λ/2 and the impedance of thepass-band frequency 2102 when viewing a balanced device from theoutput-terminal side is shifted from a matching state. For example, whenthe length of a transmission line is equal to 3λ/8, the impedance of thepassing band 2101 becomes inductive as shown in FIG. 21(a). In thiscase, as shown in FIG. 22, it is only necessary to connect thetransmission line 604 as a phase circuit and a capacitor 2202 serving asa matching circuit between output terminals of a phase circuit 2201 inparallel. As shown in FIG. 21(b), by using the above configuration, theimpedance of a pass-band vicinity 2102 when viewing a balanced devicefrom the output-terminal side becomes the center of Smith chart and itis possible to realize impedance matching. Thus, it is allowed toconstitute a phase circuit so as to include a matching circuit forperforming impedance matching.

Moreover, the fact that the length of a transmission line is equal to3λ/8 is equivalent to the fact that the phase angle is 135° andapproaches 180° by adding the above matching circuit and the length ofthe transmission line substantially approaches λ/2. Therefore, by addingthe matching circuit, it is possible to decrease the length of thetransmission line and downsize the configuration.

In the case of this embodiment, the phase circuit is constituted byusing the transmission line or three impedance elements. However, theconfiguration of a phase circuit is not restricted to the above case.Moreover, the numbers of and configurations of inductors and capacitorsserving as impedance elements are not restricted to the above case. Byusing a configuration operating as a phase circuit, the same advantageas the present invention can be obtained.

Moreover, it is allowed to form a phase circuit on a circuit substrateby using a transmission line and a chip component. It is also allowed toconstitute a phase circuit on a substrate with a balanced device mountedor in a package. Moreover, it is allowed to form a part of a phasecircuit in a laminated device constituted by forming electrode patternson a plurality of dielectric layers and laminating the dielectriclayers. Furthermore, by constituting the laminated device so as to haveanother circuit function and integrating a balanced high-frequencydevice of the present invention with the laminated device as a compositedevice, it is possible to realize a multifunctional compact balancedhigh-frequency device.

Though it is described that an input terminal is the unbalanced type andan output terminal is the balanced type in the case of this embodiment,it is allowed that the input terminal is the balanced type and theoutput terminal is the unbalanced type or both the input terminal andoutput terminal are the balanced type.

Embodiment 7

A balanced high-frequency device of embodiment 7 of the presentinvention is described below by referring to the accompanying drawings.A specific configuration when a matching circuit is included in a phasecircuit is described below. FIG. 23(a) shows a configuration of thebalanced high-frequency device of the embodiment 7 of the presentinvention. In FIG. 23(a), a balanced high-frequency device 2301 isconstituted by a balanced device 2302 and a phase circuit 2303.Moreover, in the balanced device 2302, the input-side terminal is aninput terminal IN serving as an unbalanced input/output terminal andoutput-side terminals are output terminals OUT1 and OUT2 serving asbalanced input/output terminals. Moreover, the phase circuit 2303 isconnected between the output terminals.

The phase circuit 2303 is constituted by capacitors 2304 and 2305 and aninductor 2306 serving as impedance elements and an inductor 2307 servingas a matching circuit. In this case, the output terminals OUT1 and OUT2are grounded through the capacitors 2304 and 2305 respectively, theinductor 2306 is connected between the output terminals, and the phasecircuit 2303 is connected between the output terminals. Moreover, theinductor 2307 serving as a matching circuit is included in the phasecircuit 2303.

The inductor 2306 forms a virtual ground point 2308 on adifferential-mode signal component. Therefore, the capacitor 2304 and apart of the inductor 2306 form a parallel resonant circuit to a groundplane at the output terminal OUT1 and the capacitor 2304 and a part ofthe inductor 2306 form a parallel resonant circuit to a ground plane atthe output terminal OUT2. By designing parallel resonant frequencies ofthe parallel resonant circuits so that they are kept in a passing bandor nearby the passing band, the impedance of a differential-mode signalcomponent at a predetermined frequency approaches infinity to a groundplane and transferred to an output terminal without being shorted to theground plane. That is, operations substantially same as those shown inFIG. 7(c) are executed on the differential-mode signal component.

Moreover, the inductor 2306 does not form a virtual ground point on ancommon-mode signal component. Therefore, by designing impedances of thecapacitors 2304 and 2305 serving as impedance elements arranged betweenthe balanced input/output terminals OUT1 and OUT2 and ground planes tosufficiently small values, the common-mode signal component is shortedto a ground plane and thereby, it is not transferred to a balancedinput/output terminal.

As described above, in the case of the phase circuit 2303 of thisembodiment, a resonant circuit at a predetermined frequency isconstituted by the capacitors 2304 and 2305 and the inductor 2306 andthe inductor 2307 serving as a matching circuit is included. Also inthis case, common-mode signal components are reduced and it is possibleto realize a balanced high-frequency device having excellentbalance-characteristics.

Moreover, it is possible to incorporate the inductor 2307 into theinductor 2306. That is, it is enough to use a combined inductance 2309of the inductors 2306 and 2307. In this case, because the inductors 2306and 2307 are connected in parallel, the expression Lt=(Lb×Lm)/(Lb+Lm) iseffectuated when assuming inductances of the inductors 2306 and 2307 andcombined inductor 2309 as Lb, Lm, and Lt respectively. Thus, it ispossible to decrease values of the inductances. Moreover, it is possibleto decrease the number of devices and downsize a circuit configuration.

In this case, however, the meaning of a predetermined frequency differs.That is, when assuming capacitances of the capacitors 2304 and 2305 asCg1 and Cg2, parallel resonant frequencies f1 and f2 ofdifferential-mode signal components at each output terminal in amatching state formed by the capacitors 2304 and 2305 and inductor 2306become f1=1/{2π×{square root}(Lb/2)×{square root}(Cg1)} andf2=1/{2π×{square root}(Lb/2)×{square root}(Cg2)}. In this case, byincluding the inductor 2307 serving a matching circuit, the wholeparallel resonant frequencies f1 t and f2 t become fit=1/{2π×{squareroot}(Lt/2)×{square root}(Cg1)} and f2t=1/{2π{square root}(Lt/2)×{squareroot}(Cg2)} and thus, they are apparently shifted from predeterminedfrequencies.

That is, the whole parallel resonant frequency of the phase circuit 2303is shifted from a pass band or the vicinity of the pass band by a valueequivalent to the inductor Lm. However, the effect that common-modesignal component can be reduced is the same when the capacitor 2304 anda part of the inductor 2306 form a parallel resonant circuit to a groundplane at the output terminal OUT1 and the capacitor 2305 and a part ofthe inductor 2306 form a parallel resonant circuit to a ground plane ina matching state and the impedance to ground planes of the capacitors2304 and 2305 are sufficiently small. In this case, a part of theinductor 2306 denotes a range up to a virtual ground plane.

However, the circuit configuration of this embodiment is not restrictedto the above case. As long as operations of a matching circuit andoperations of a resonant circuit are substantially the same as the caseof the present invention, it is possible to realize a balancedhigh-frequency device having excellent balance-characteristics similarlyto the case of the present invention.

Moreover, though values Cg1 and Cg2 of capacitors serving as impedanceelements are assumed to be substantially the same and values Lg1 and Lg2of inductors serving as impedance elements are assumed to besubstantially the same, it is not always necessary that these values arethe same but they are optimally selected in accordance with a circuitconfiguration.

Embodiment 8

A balanced high-frequency device of embodiment 8 of the presentinvention is described below by referring to the accompanying drawings.Specific characteristics of the balanced high-frequency device aredescribed below on a case of using an surface acoustic wave filter as abalanced device. FIG. 24 shows a configuration of a balancedhigh-frequency device 2401 of the present invention. In FIG. 24, thebalanced high-frequency device 2401 is constituted by an surfaceacoustic wave filter 2402 serving as a balanced device and a phasecircuit 2403. Moreover, in the case of the surface acoustic wave filter2402, the input-side terminal is an input terminal IN serving as anunbalanced input/output terminal and output-side terminals are outputterminals OUT1 and OUT2 serving as balanced input/output terminals.Moreover, the phase circuit 2403 is connected between the outputterminals.

The surface acoustic wave filter 2402 is formed on a piezoelectricsubstrate 2404 by first, second, and third inter-digital transducerelectrodes (hereafter respectively referred to as IDT electrode) 2405,2406, and 2407 and first and second reflector electrodes 2408 and 2409.The first IDT electrode 2405 is divided into two divided IDT electrodesand one-hand electrode fingers of the first and second divided IDTelectrodes 2410 and 2411 are connected to the output terminals OUT1 andOUT2. The other-hand electrode fingers of the first and second dividedIDT electrodes 2410 and 2411 are electrically connected and virtuallygrounded. Moreover, one-hand electrode fingers of the second and thirdIDT electrodes 2406 and 2407 are connected to the input terminal IN andthe other-hand electrode fingers of them are grounded. By using theabove configuration, it is possible to obtain a balanced high-frequencydevice having an unbalance-balanced input/output terminal.

Also in the case of the balanced high-frequency device 2401 of theembodiment 8 of the present invention, it is possible to reducecommon-mode signal components by using the phase circuit 2403 andrealize a balanced high-frequency device excellent inbalance-characteristic.

In the case of this embodiment, it is also allowed to constitute a phasecircuit by using a transmission line or three impedance elements.Moreover, a configuration of the phase circuit is not restricted to theabove one. By using a configuration operating as a phase circuit, thesame advantage as the present invention can be obtained. Moreover, thenumbers of and configurations of inductors and capacitors serving asimpedance elements are not restricted to the above mentioned. By using aconfiguration operating as a phase circuit, the same advantage as thepresent invention is obtained.

Moreover, it is allowed to form a phase circuit on a circuit substrateby using a transmission line and a chip component or form the phasecircuit on a substrate with a balanced device mounted or in a package.Furthermore, it is allowed to form a part of the phase circuit in alaminated device constituted by forming electrode patterns on aplurality of dielectric layers and laminating the dielectric layers.Furthermore, by constituting the laminated device so as to have anothercircuit function and integrating the laminated device with a balancedhigh-frequency device of the present invention as a composite device, itis possible to realize a multifunctional compact balanced high-frequencydevice.

Though it is described that an input terminal is the unbalanced type andan output terminal is the balanced type in the case of this embodiment,it is allowed that the input terminal is the balanced type and theoutput terminal is the unbalanced type. Moreover, it is allowed thatboth the input and output terminals are the balanced type.

Embodiment 9

A balanced high-frequency device of embodiment 9 of the presentinvention is described below by referring to the accompanying drawings.Specific characteristics of the balanced high-frequency device aredescribed below on a case of using an surface acoustic wave filter as abalanced device. FIG. 25 shows a configuration of a balancedhigh-frequency device 2501 of the embodiment 9 of the present invention.In FIG. 25, the balanced high-frequency device 2501 is constituted by ansurface acoustic wave filter 2502 serving as a balanced device and aphase circuit 2503. Moreover, in the case of the surface acoustic wavefilter 2502, the input-side terminal is an input terminal IN serving asan unbalanced input/output terminal and output-side terminals are outputterminals OUT1 and OUT2 serving as balanced terminals. Furthermore, thephase circuit 2503 is connected between the output terminals.

The surface acoustic wave filter 2502 is formed on a piezoelectricsubstrate 2504 by first, second, and third inter-digital transducerelectrodes (hereafter respectively referred to as IDT electrode) 2505,2506, and 2507 and first and second reflector electrodes 2508 and 2509.One-hand electrode finger of the first IDT electrode is connected to theinput terminal IN and the other-hand electrode finger of it is grounded.One-hand electrode fingers of the second and third IDT electrodes 2506and 2507 are connected to the output terminals OUT1 and OUT2 and theother-hand electrode fingers of them are grounded. By using the aboveconfiguration, a balanced high-frequency device having anunbalanced-balanced input/output terminal is obtained.

Also in the case of the balanced high-frequency device 2501 of thepresent invention, it is possible to reduce common-mode signalcomponents by using the phase circuit 2503 and therefore, realize abalanced high-frequency device excellent in balance-characteristic.

In the case of this embodiment, a phase circuit is provided by using atransmission line or three impedance elements. Moreover, a configurationof the phase circuit is not restricted to the above case. By using aconfiguration operating as a phase circuit, the same advantage as thepresent invention is obtained. Furthermore, the numbers of andconfigurations of inductors and capacitors serving as impedance elementsare not restricted to the above case. By using a configuration operatingas a phase circuit, the same advantage as the present invention isobtained.

Furthermore, a phase circuit may be formed on a circuit substrate byusing a transmission line or a chip component or integrate the phasecircuit on a substrate with a balanced device mounted or in a package.Furthermore, a part of the phase circuit may be formed in a laminateddevice constituted by forming electrode patterns on a plurality ofdielectric layers and laminating the dielectric layers. Furthermore, byforming the laminated device so as to have another circuit function andintegrating a balanced high-frequency device of the present inventionwith the laminated device as a composite device, it is possible torealize a multifunctional compact balanced high-frequency device.

Though it is described that an input terminal is the unbalanced type andan output terminal is the balanced type in the case of this embodiment,the input terminal may be the balanced type and the output terminal theunbalanced type. Moreover, both the input and output terminals may bethe balanced type.

Embodiment 10

A balanced high-frequency device of embodiment 10 of the presentinvention is described below by referring to the accompanying drawings.FIG. 26 shows a configuration of a balanced high-frequency device 2601of the embodiment 10 of the present invention. For FIG. 26, a specificconfiguration of the balanced high-frequency device is described on acase of using a semiconductor device as the balanced device. In FIG. 26,the balanced high-frequency device 2601 is constituted by asemiconductor device 2602 serving as a balanced device and phasecircuits 2603 and 2608. Moreover, in the case of the semiconductordevice 2602, input-side terminals are input terminals IN1 and IN2serving as balanced input/output terminals and output-side terminals areoutput terminals OUT1 and OUT2 serving as balanced terminals.Furthermore, the phase circuit 2603 is connected between the inputterminals and the phase circuit 2608 is connected between the outputterminals.

Then, a configuration of the semiconductor device 2602 is describedbelow. Symbols 2604 a, 2604 b, 2605 a, and 2605 b denote bipolartransistors and 2606 a and 2606 b denote inductors. The input terminalIN1 is connected to the base of the bipolar transistor 2604 a through aDC-cut capacitor 2607 a and the input terminal IN2 is connected to thebase of the bipolar transistor 2604 b through a DC-cut capacitor 2607 b.Collectors of the bipolar transistors 2604 a and 2604 b are connected toemitters of the bipolar transistors 2605 a and 2605 b respectively andcollectors of the bipolar transistors 2605 a and 2605 b are connected tothe output terminals OUT1 and OUT2 through DC-cut capacitors 2609 a and2609 b respectively. Emitters of the bipolar transistors 2604 a and 2604b are grounded through the inductors 2606 a and 2606 b respectively. Abias circuit 2610 supplies a bias current to bases of the bipolartransistors 2604 a and 2604 b. A bias circuit 2611 supplies a biascurrent to bases of the bipolar transistors 2605 a and 2605 b. Apower-source voltage Vcc is supplied to collectors of the bipolartransistors 2605 a and 2605 b through choke inductors 2912 a and 2912 brespectively. By using the above configuration, a balanced semiconductordevice operates as an amplifier.

Also in the case of the balanced high-frequency device 2601 of theembodiment 10 of the present invention, it is possible to reducecommon-mode signal components by using the phase circuits 2603 and 2608and therefore, realize a balanced high-frequency device excellent inbalance-characteristic.

In this embodiment, a phase circuit may be formed by using atransmission line or three impedance elements. Moreover, a configurationof the phase circuit is not restricted to the above case. By using aconfiguration operating as a phase circuit, the same advantage as thepresent invention is obtained. Furthermore, the numbers of andconfigurations of inductors and capacitors serving as impedance elementsare not restricted to the above case. By using a configuration operatingas a phase circuit, the same advantage as the present invention isobtained.

A phase circuit on a circuit maybe formed on a circuit substrate byusing a transmission line or a chip component or integrate the phasecircuit on a substrate with a balanced device mounted or in a package.Moreover, apart of the phase circuit may be formed in a laminated deviceby forming electrode patterns on a plurality of dielectric layers andlaminating the dielectric layers. Furthermore, by forming the laminateddevice so as to have another circuit function and integrating a balancedhigh-frequency device of the present invention with the laminated deviceas a composite device, it is possible to realize a multifunctionalcompact balanced high-frequency device.

Furthermore, in the case of this embodiment, it is described that inputand output terminals are the balanced type. However, either of the inputand output terminals may be the unbalanced type and the other of them isthe balanced type.

Furthermore, in the case of this embodiment, a semiconductor device isformed by four bipolar transistors. However, a configuration of thesemiconductor device is not restricted to the above case.

Furthermore, for this embodiment, a case is described in which thesemiconductor device 2602 is an amplifier. However, the semiconductordevice 2602 is not restricted to an amplifier. The semiconductor device2602 may be a mixer or oscillator. In short, the semiconductor device2602 is permitted as long as it is a semiconductor device having abalanced terminal.

Embodiment 11

A balanced high-frequency circuit of embodiment 11 of the presentinvention is described below by referring to the accompanying drawings.FIG. 27 is a block diagram of a balanced high-frequency circuit 2701using a balanced device of the present invention. In FIG. 27, an outputsignal output from a transmitting circuit is transmitted from an antenna2705 through a transmitting amplifier 2702, a transmitting filter 2703and a switch 2704. Moreover, an input signal received through theantenna 2705 is input to a receiving circuit through the switch 2704, areceiving filter 2706, and a receiving amplifier 2707. In this case,because the transmitting amplifier 2702 is the balanced type and theswitch 2704 is the unbalanced type, the transmitting filter 2703 isconstituted so as to have an unbalanced-balanced input/output terminal.Furthermore, because the receiving amplifier 2707 is the balanced typeand the switch 2704 is the unbalanced type, the receiving filter 2706 isconstituted so as to have an unbalanced-balanced input/output terminal.

By applying a balanced device of the present invention to thetransmitting filter 2703 or receiving filter 2706 of the balancedhigh-frequency circuit 2701 and a balanced high-frequency device of thepresent invention to the transmitting amplifier 2702 or receivingamplifier 2707, it is possible to prevent modulation accuracydeterioration at the time of transmission due to deterioration of abalance-characteristic and sensitivity deterioration at the time ofreception due to deterioration of a balance-characteristic and realize ahigh-performance balanced high-frequency circuit.

Moreover, when the switch 2704 is the balanced type and the transmittingamplifier 2702 or receiving amplifier 2707 is the unbalanced type, thesame advantage is obtained by replacing balanced-type andunbalanced-type input/output terminals of the transmitting filter 2703or receiving filter 1006 with each other.

Though means of switching transmission and reception is described byusing the switch 2704 in the case of the balanced high-frequency circuit2701, the means may use a shared unit.

Moreover, a phase circuit of the present invention may be formed on acircuit substrate in the case of the balanced high-frequency circuit ofthis embodiment. For example, in FIG. 27, by forming the phase circuitbetween balanced transmission lines 2708 and 2709 on the circuitsubstrate, it is possible to prevent balance-characteristicdeterioration due to the crosstalk of common-mode signal components andrealize a excellent balanced high-frequency circuit.

Furthermore, embodiments of the present invention are described by usingan surface acoustic wave filter or semiconductor device as a balancedhigh-frequency device. However, the present invention can be applied notonly to the above case but also to another device whichbalance-operates.

Furthermore, on a device for handling a high-frequency signal, parasiticcomponents increase as a frequency rises, common-mode signal componentincrease due to crosstalk, and deterioration of balance-characteristicsincreases. Therefore, advantages of a balanced high-frequency device ofthe present invention increase as a frequency rises and it is possibleto downsize a transmission line and an impedance element for forming aphase circuit.

As described above, the present invention makes it possible to provide abalanced high-frequency device having preferablebalance-characteristics, balanced high-frequency circuit, phase circuit,and balance-characteristics improving method.

Embodiment 12

Specific characteristics of a balanced high-frequency filter of thepresent invention are described below by referring to the accompanyingdrawings.

FIGS. 33(a) to 33(c) are characteristics of a balanced high-frequencydevice 1401 when using the phase circuit 1201 shown in FIG. 12 as aphase circuit 1403. In this case, inductances L1 and L2 of inductors1202 and 1203 are substantially the same value. The capacity C of acapacitor 1204 is set so that its impedance becomes 167 Ωin a frequencyin a passing band. Moreover, series resonant frequencies of L1 and C/2and L2 and C/2 are set so that they are kept in the passing band.

In FIGS. 33(a) to 33(c), FIG. 33(a) is a passing characteristic, FIG.33(b) is an amplitude balance characteristic of a passing band, and FIG.33(c) is a phase balance characteristic of the passing band. The balancecharacteristics are greatly improved compared to the conventionalcharacteristics shown in FIGS. 32(a) to 32(c), providing substantiallyideal characteristics.

Then, a case in which impedances of the inductors 1202 and 1203 arechanged is evaluated. FIGS. 34(a) and 34(b) show balance characteristicsto the normalized impedance obtained by dividing impedances of theinductors 1202 and 1203 by the characteristic impedance of a terminal.In this case, because the characteristic impedance of balanced outputterminal is 50 Ω, the characteristic impedance of each terminal is setto 25 Ω. In FIGS. 34(a) and 34(b), FIG. 34(a) is an amplitude balancecharacteristic and FIG. 34(b) is a phase balance characteristic.Moreover, numerical values 3401 and 3402 denote the maximum value andthe minimum value of deterioration of the amplitude balancecharacteristic in a passing band of the surface acoustic wave filter ofthis embodiment and 3403 and 3404 denote the maximum value and theminimum value of deterioration of the phase balance characteristic in apassing band of the surface acoustic wave filter of this embodiment.Furthermore, broken lines show the maximum value and the minimum valueof deterioration of the balance characteristic of a conventional surfaceacoustic wave filter. From FIGS. 34(a) and 34(b), it is found that thebalance characteristic is improved when the normalized impedance is 50or less.

Furthermore, FIG. 35 shows loss characteristic of a passing band to thenormalized impedance obtained by dividing impedances of the inductors1202 and 1203 by the characteristic impedance of a terminal.Furthermore, a broken line shows the value of the loss of a conventionalsurface acoustic wave filter. From FIG. 35, it is found that the loss isdeteriorated in a range in which the normalized impedance is smallerthan 3. This is because when the inductance of an inductor is small, theimpedance relating to a differential signal component becomes small andthe differential signal component is short-circuited. Therefore, it ispreferable to set the normalized impedance in a passing band to 3 ormore.

Then, a characteristic when using a phase circuit having still anotherconfiguration is shown. FIGS. 36(a) to 36(c) show characteristics of thebalanced high-frequency device 1401 when using the phase circuit 1301shown in FIG. 13 as the phase circuit 1403. In this case, the capacitiesC1 and C2 of the capacitors 1302 and 1303 are substantially the same.The inductance L of the inductor 1304 is designed so that the impedanceof the inductor 1304 becomes 167 Ω in the frequency in a passing band.Moreover, series resonant frequencies of C1 and 2×L and C2 and 2×L aredesigned so that they are kept in a passing band.

In FIGS. 36(a) to 36(c), FIG. 36(a) is a passing characteristic, FIG.36(b) is an amplitude balance characteristic of the passing band, andFIG. 36(c) is a phase balance characteristic of the passing band.Compared with the conventional characteristic indicated in FIG. 32, thebalance characteristics are greatly improved and become characteristicsalmost close to an ideal state.

Then, a case in which impedances of the capacitors 1302 and 1303 arechanged is evaluated. FIGS. 37(a) and 37(b) show balance characteristicsto the normalized impedance obtained by dividing the impedances of thecapacitors 1302 and 1303 by the characteristic impedance of a terminal.In this case, because the balance characteristic of each balanced outputterminals is 50 Ω, the characteristic impedance of each terminal is setto 25 Ω. In FIGS. 37(a) and 37(b), FIG. 37(a) is an amplitude balancecharacteristic and FIG. 37(b) is a phase balance characteristic.Moreover, reference numerals 3701 and 3702 are the maximum value and theminimum value of deterioration of the amplitude balance characteristicin a passing band in the surface acoustic wave filter of this embodimentand reference numerals 3703 and 3704 are the maximum value and theminimum value of deterioration of the phase balance characteristic in apassing band of the surface acoustic wave filter of this embodiment.Moreover, broken lines show the maximum value and the minimum value ofdeterioration of the balance characteristic of a conventional surfaceacoustic wave filter. From FIGS. 37(a) and 37(b), it is found that thebalance characteristic is improved in a range in which the normalizedimpedance is 50 or less.

Furthermore, FIG. 38 shows the characteristic of the loss of a passingband to the normalized impedance obtained by dividing impedances of thecapacitors 1302 and 1303 by the characteristic impedance of a terminal.Furthermore, a broken line shows the value of the loss of a conventionalsurface acoustic wave filter. From FIG. 38, it is found that the loss isdeteriorated in a range in which the normalized impedance is smallerthan 3. This is because when the inductance of an inductor is small, theimpedance relating to a differential signal component becomes small andthe differential signal component is short-circuited. Therefore, it ispreferable to set the normalized impedance in a passing band to 3 ormore.

As described above, in the case of the embodiment 11 of the presentinvention, by setting normalized impedances of the inductors 1202 and1203 and capacitors 1302 and 1303 to 50 or less, it is possible toimprove balance characteristics and moreover, by setting the normalizedimpedance to 3 or more, it is possible to restrain a loss fromdeteriorating.

Moreover, in the case of this embodiment, the characteristic of asurface acoustic wave filter is described by way of example, and notlimitation. In the case of the present invention, an in-phase signalcomponent output from a balanced element is decreased by a phase shiftcircuit. Therefore, when a balanced element has a balanced terminal, thesame effect can be obtained. As the balanced element, it is also allowedto use a filter using a FBAR. FIG. 39 shows a block diagram of the FBAR.In FIG. 39, the FBAR 3901 is constituted by including a lower electrode3903, piezoelectric thin film 3904, and upper electrode 3805 formed on asubstrate 3902. A cavity 3906 is formed on the substrate 3902 below thelower electrode. Thereby, an energy confinement resonator is realized.In this case, the lower electrode 3903 and upper electrode 3905correspond to the input/output electrode of a single FBAR. Si orsapphire is used for the substrate 3902. Moreover, Al, Mo, Au, Cu, or Tiis used for the lower electrode 3903 and upper electrode 3905.Furthermore, AlN or ZnO is used for the piezoelectric thin film 3904. Byusing the above configuration, an FBAR is constituted. By applying aladder filter or a mode coupling filter using the FBAR to a balancedhigh-frequency element of the present invention, the effect same as thatof the present invention is obtained as a balanced high-frequencyfilter. Moreover, the configuration of the FBAR is not restricted to theabove mentioned. For example, it is allowed to use a configuration usingan acoustic mirror. Furthermore, even if applying the aboveconfiguration to a semiconductor device having a balanced terminal suchas a low-noise amplifier or mixer, the same effect can be obtained.

Furthermore, in the case of this embodiment, the resonance frequency ofa series resonant circuit to an in-phase signal component is kept in apassing band. However, even if this is kept nearby the passing band, thesame effect can be obtained.

1. A balanced high-frequency device comprising: a balanced element; atleast one balanced terminal connected to the balanced element; a phasecircuit having at least first, second, and third impedance elements, andelectrically connected between the balanced element and the balancedterminals; wherein the first impedance element and the second impedanceelement are connected between the balanced terminals in series, theconnection point between the first impedance element and the secondimpedance element is grounded through the third impedance element, aseries resonant circuit is formed by the first impedance element and thethird impedance element, a series resonant circuit is formed by thesecond impedance element and the third impedance element, and animpedance to a differential signal component in the passing band of thebalanced element of the first and second impedance elements is set so asto increase to the ground plane.
 2. The balanced high-frequency deviceaccording to claim 1, wherein the first and second impedance elementsare capacitors, and the third impedance element is an inductor.
 3. Thebalanced high-frequency device according to claim 1, wherein the firstand second impedance elements are inductors, and the third impedanceelement is a capacitor.
 4. The balanced high-frequency device accordingto claim 1, wherein an impedance in the passing band of the balancedelement of the first and second impedance elements is set so that avalue standardized by the characteristic impedance value of either ofthe balanced terminals becomes 3 or more.
 5. The balanced high-frequencydevice according to claim 1, wherein an impedance in the passing band ofthe balanced element of the first and second impedance elements is setso that a value standardized by the characteristic impedance value ofeither of the balanced terminals becomes 50 or less.
 6. The balancedhigh-frequency device according to claim 1, wherein an impedance in thepassing band of the balanced elements of the first and second impedanceelements is set so that a value normalized by the characteristicimpedance value of either of the balanced terminals ranges between 3 and50.
 7. The balanced high-frequency device according to any one of claims1 to 6, wherein the balanced elements are surface acoustic wave filters,the surface acoustic wave filters respectively have a piezoelectricsubstrate and IDT electrodes serving as a plurality of inter-digitaltransducer electrodes formed on the piezoelectric substrate, and atleast one of the IDT electrodes is connected to a balanced inputterminal or balanced output terminal.
 8. The balanced high-frequencydevice according to claim 7, wherein each of the surface acoustic wavefilters is a longitudinal-mode (coupled) surface acoustic wave filter inwhich at least first, second, and third IDT electrodes are arrangedalong the propagation direction of a surface acoustic wave, the secondand third IDT electrodes are arranged at both sides of the first IDTelectrode, the first IDT electrode is the balanced type, and one and another electrode fingers constituting the first IDT electrode areconnected to balanced input terminals or balanced output terminals. 9.The balanced high-frequency device according to claim 7, wherein thesurface acoustic wave filters are longitudinal-mode (coupled) surfaceacoustic wave filters in which at least first, second, and third IDTelectrodes are arranged along the propagation direction of a surfaceacoustic wave, the second and third IDT electrodes are arranged at bothsides of the first IDT electrode, the fist IDT electrode is constitutedof a plurality of split IDT electrodes, and at least two of the splitIDT electrodes are connected to a balanced input terminals or balancedoutput terminals.
 10. The balanced high-frequency device according toclaim 7, wherein the surface acoustic wave filters are longitudinal-mode(coupled) surface acoustic wave filters in which at least first, second,and third IDT electrodes are arranged along the propagation direction ofa surface acoustic wave, the second and third IDT electrodes arearranged at both sides of the first IDT electrode, the second IDTelectrode is connected to either of balanced input terminals or eitherof balanced output terminals, and the third IDT electrode is connectedto the other of the balanced input terminals or the other of thebalanced output terminals.
 11. The balanced high-frequency deviceaccording to any one of claims 1 to 6, wherein the balanced element isconstituted of a filter using a FBAR.
 12. A balanced high-frequencycircuit having the balanced high-frequency device according to any oneof claims 1 to
 6. 13. The balanced high-frequency circuit according toclaim 12, wherein the balanced high-frequency device of claim 7 is usedfor a transmitting filter and/or receiving filter constituting thebalanced high-frequency circuit.
 14. The balanced high-frequency circuitaccording to claim 12, wherein the balance high-frequency device ofclaim 11 is used for a transmitting filter and/or receiving filterconstituting the balanced high-frequency circuit.
 15. A balancedhigh-frequency circuit comprising: a circuit board; and balancedtransmission lines on the circuit board, wherein the phase circuit ofany one of claims 1 to 6 is connected between the balanced lines.
 16. Aphase circuit to be connected between balanced terminals or balancedlines, comprising: at least first, second, and third impedances; whereinthe first impedance element and the second impedance element areconnected between the balanced terminals or balanced lines in series,the connection point between the first impedance element and the secondimpedance element is grounded through the third impedance element, aseries resonant circuit includes the first impedance element and thethird impedance element, a series resonant circuit includes the secondimpedance element and the third impedance element, and an impedance to adifferential signal component in the passing band of the balancedelements of the first and second impedance elements is set so as toincrease to the ground plane.
 17. The phase circuit according to claim16, wherein an impedance in a desired passing band of the first andsecond impedance elements is set so that a value normalized by acharacteristic impedance value of either of the balanced terminalsbecomes 3 or more.
 18. The phase circuit according to claim 16, whereinan impedance in a desired passing band of the first and second impedanceelements is set so that a value normalized by a characteristic impedancevalue of either of the balanced terminals becomes 50 or less.
 19. Thephase circuit according to claim 16, wherein an impedance in a desiredpassing band of the first and second impedance elements is set so that avalue normalized by a characteristic impedance value of either of thebalanced terminals ranges between 3 and 50.